A 28-year-old man presents with a 6-week history of bloody diarrhea, abdominal cramping, and urgency. Colonoscopy reveals continuous mucosal inflammation limited to the colon with crypt distortion and surface ulceration. Histology confirms acute and chronic inflammation. He is diagnosed with ulcerative colitis and is now being initiated on induction therapy. What is the drug of choice for inducing remission in this patient?

Question

Accepted Answer

A. Mesalamine (5-ASA). ## First-Line Induction Therapy in Ulcerative Colitis

**Key Point:** Mesalamine (5-aminosalicylic acid) is the first-line agent for inducing remission in mild-to-moderate ulcerative colitis, both as monotherapy and in combination with topical agents.

### Mechanism of Action
- Anti-inflammatory effect via inhibition of nuclear factor-kappa B (NF-κB)
- Reduces prostaglandin synthesis and leukocyte recruitment
- Acts locally on colonic mucosa

### Dosing and Route in UC
- **Oral:** 2–4 g daily in divided doses (maintenance: 1.5–2.4 g daily)
- **Topical (rectal):** Enema or suppository for distal disease
- **Combination:** Oral + topical for better efficacy in moderate disease

### Efficacy Data
- Remission induction rate: 40–50% in mild-to-moderate UC
- Superior to placebo in multiple RCTs
- Also effective for maintenance of remission

### When to Escalate

| Disease Severity | First-Line | Second-Line |
|---|---|---|
| Mild-moderate | 5-ASA (oral ± topical) | Add corticosteroids |
| Moderate-severe | 5-ASA + corticosteroids | Add biologics (TNF-α inhibitors) |
| Severe/fulminant | IV corticosteroids ± biologics | Consider colectomy |

**High-Yield:** Mesalamine is safe, well-tolerated, and effective for both induction and maintenance in UC. It is NOT effective in Crohn's disease.

**Clinical Pearl:** Topical mesalamine (enema) penetrates 15–20 cm proximally; suppository reaches only the rectosigmoid. Combination therapy (oral + topical) is superior to oral alone in distal/left-sided disease.

### Monitoring
- Baseline renal function (rare nephrotoxicity)
- Clinical response at 4–6 weeks
- If inadequate response → add corticosteroids or escalate to biologics

[cite:Harrison 21e Ch 297]

Answer

B. Infliximab

Answer

C. Budesonide

Answer

D. Azathioprine

Explanation

First-Line Induction Therapy in Ulcerative Colitis

Mechanism of Action

Dosing and Route in UC

Efficacy Data

When to Escalate

Monitoring

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Disease Severity	First-Line	Second-Line
Mild-moderate	5-ASA (oral ± topical)	Add corticosteroids
Moderate-severe	5-ASA + corticosteroids	Add biologics (TNF-α inhibitors)
Severe/fulminant	IV corticosteroids ± biologics	Consider colectomy